Inspection for alignment between IC die and package substrate

ABSTRACT

In a method and system for inspecting alignment between an IC (integrated circuit) die and a package substrate, a plurality of fiducials are located on the package substrate for determining a plurality of references. A center point of the package substrate is determined from the plurality of references. In addition, whether a center point of the IC die is aligned to the center point of the package substrate within an acceptable range is determined.

TECHNICAL FIELD

The present invention relates generally to integrated circuitmanufacture, and more particularly, to a method and system forinspection of alignment between an IC (integrated circuit) die and apackage substrate using fiducials.

BACKGROUND OF THE INVENTION

Referring to FIG. 1, during manufacture of an IC (integrated circuit)package 100, an IC die 102 is mounted onto a package substrate 104. Forexample, the IC package 100 may be a C4 IC package available fromAdvanced Micro Devices, Inc. having its principal place of business atSunnyvale, Calif. Solder bumps 106A, 106B, and 106C are mounted to pads108A, 108B, and 108C, respectively, for coupling nodes of the integratedcircuit fabricated on the IC die 102 to leads (not shown in FIG. 1) ofthe package substrate 104. Such leads provide external access to thenodes of the integrated circuit fabricated on the IC die 102.

FIG. 2 shows a view of an upper surface 110 of the package substrate 104having a plurality of circular pads 108A, 108B, 108C, 108D, 108E, 108F,108G, 108H, and 108I exposed thereon. An area 112 (outlined in dashedlines in FIG. 2) of the package substrate 104 having such a plurality ofpads therein is termed a “cage” of the package substrate 104. FIG. 1illustrates a cross-sectional view of the package substrate 104 acrossline I—I in FIG. 2.

FIG. 3 shows a view of a bottom surface 114 of the IC die 102 having aplurality of solder bumps 106A, 106B, 106C, 106D, 106E, 106F, 106G,106H, and 1061 formed thereon. FIG. 1 illustrates a cross-sectional viewof the IC die 102 across line II—II in FIG. 3. Referring to FIGS. 1, 2,and 3, the IC die 102 is placed onto the package substrate 104 with thebottom surface 114 of the IC die 102 facing the top surface 110 of thepackage substrate 104.

The solder bumps 106A, 106B, 106C, 106D, 106E, 106F, 106G, 106H, and106I of the IC die 102 are desired to be coupled to the pads 108A, 108B,108C, 108D, 108E, 108F, 108G, 108H, and 108I, respectively, of thepackage substrate 104. Such solder bumps of the IC die 102 are coupledto such pads of the package substrate 104 via solder joints formed fromthe solder bumps in a reflow process, as known to one of ordinary skillin the art. An IC die and a package substrate typically have morenumerous solder bumps and pads, respectively. However, nine solder bumpsand nine pads are illustrated and described herein for the IC die 102and package substrate 104 for simplicity and clarity of illustration.

For coupling with minimized resistance between the solder bumps of theIC die 102 and the pads of the package substrate 104, the respectivecenter point of each of the solder bumps 106A, 106B, 106C, 106D, 106E,106F, 106G, 106H, and 106I is desired to be aligned to the respectivecenter point of each of the pads 108A, 108B, 108C, 108D, 108E, 108F,108G, 108H, and 1081, respectively. Such alignment is illustrated with adashed line 116 in FIG. 1 through the centers of the example solder bump106B and the example corresponding pad 108B.

FIG. 4 illustrates the scenario when the IC die 102 is shiftedundesirably too much to the left by a first misaligned displacement 118.Similarly, FIG. 5 illustrates the scenario when the IC die 102 isshifted undesirably too much to the right by a second misaligneddisplacement 120. Generally, the IC die 102 may be misaligned withrespect to the package substrate 104 in any of a plurality of directionswhen the centers of the solder bumps of the IC die 102 are not alignedto the centers of the pads of the package substrate 104.

In any case of unacceptable misalignment, undesirably high resistancesor even open circuits may result with such misaligned coupling betweenthe solder bumps of the IC die 102 and the circular pads of the packagesubstrate 104. In the example of FIGS. 2 and 3, each of the solder bumps106A, 106B, 106C, 106D, 106E, 106F, 106G, 106H, and 106I of the IC die102 and each of the circular pads 108A, 108B, 108C, 108D, 108E, 108F,108G, 108H, and 108I of the package substrate 104 has a diameter 122 ofabout 100 μm (micrometers).

For proper operation of the IC package 100, each solder bump of the ICpackage 102 is desired to be aligned with a corresponding pad of thepackage substrate 104 with any misalignment being less than 10 μm(micrometers). Thus, a mechanism is desired for placing the IC die 102onto the package substrate 104 with a desired level of alignment.

After placement of the IC die 102 onto the package substrate 104 withdesired alignment, the IC die 102 is attached to the package substrate104. Thereafter, a reflow process is performed for the IC die 102 andthe package substrate 104 such that solder bumps of the IC die 102become molten to be electrically connected to the pads of the packagesubstrate 104. Such a reflow process is typically irreversible as knownto one of ordinary skill in the art. On the other hand, even after theIC die 102 is attached to the package substrate 104, if the IC die 102is deemed to be unacceptably misaligned to the package substrate 104,the IC die 102 may be removed from the package substrate 104 before thereflow process to be better aligned to the package substrate 104. Thus,a mechanism is desired for inspection of the alignment for the IC dieattached to the package substrate before the reflow process.

SUMMARY OF THE INVENTION

Accordingly, in a general aspect of the present invention, fiducialscomprised of dots are used for automated inspection for alignmentbetween the IC die and the package substrate after attachment and beforereflow.

In a method and system for inspecting alignment between an IC(integrated circuit) die and a package substrate, a plurality offiducials are located on the package substrate for determining aplurality of references. A center point of the package substrate isdetermined from the plurality of references. In addition, whether acenter point of the IC die is aligned to the center point of the packagesubstrate within an acceptable range is determined.

According to another aspect of the present invention, each of thefiducials is comprised of a plurality of markings such as a plurality ofdots. For example, each of the first and second fiducials is comprisedof dots having a same diameter as circular pads of the packagesubstrate.

In one example embodiment of the present invention, the first and secondfiducials are disposed toward diagonally opposite corners of the packagesubstrate. In another embodiment of the present invention, a thirdfiducial with a third reference is disposed toward a third corner of thepackage substrate. In that case, the center of the package substrate isdetermined from the first, second, and third references.

In another embodiment of the present invention, the first fiducial iscomprised of a corner dot and two side dots, with each side dot beingdisplaced from the corner dot with a first distance. In that case, acenter of the corner dot is the first reference for the first fiducial.Similarly, the second fiducial is comprised of a corner dot and two sidedots, with each side dot being displaced from the corner dot with asecond distance. In that case, a center of the corner dot for the secondfiducial is the second reference.

In another aspect of the present invention, the first fiducial isdistinguishable from the second fiducial when the first distance of theside dots from the corner dot for the first fiducial is different fromthe second distance of the side dots from the corner dot for the secondfiducial.

In yet another embodiment of the present invention, an alarm isgenerated when the center point of the IC die is not aligned to thecenter point of the package substrate within the acceptable range toprevent reflow of the IC die onto the package substrate.

In a further embodiment of the present invention, whether the IC die isrotationally aligned to the package substrate within an acceptablerotational range is also determined. If the center points of the IC dieand the package substrate are aligned within the acceptable range and ifthe IC die and the package substrate are rotationally aligned within theacceptable rotation range, then the reflow process is performed forelectrically connecting solder bumps of the IC die onto pads of thepackage substrate.

In this manner, the fiducials on the package substrate are used by arobotic vision tool for automated and accurate inspection for alignmentof the IC die and the package substrate.

These and other features and advantages of the present invention will bebetter understood by considering the following detailed description ofthe invention which is presented with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of an IC die to be placed onto apackage substrate during manufacture of an IC package, according to theprior art;

FIG. 2 shows a view of a top surface of the package substrate having aplurality of circular pads exposed thereon, according to the prior art;

FIG. 3 shows a view of a bottom surface of the IC die having a pluralityof solder bumps formed thereon, according to the prior art;

FIGS. 4 and 5 illustrate the cross-sectional view of FIG. 1 withmisalignment between the IC die and the package substrate in a pluralityof directions, according to the prior art;

FIG. 6 illustrates a block diagram of a system for placing an IC dieonto a package substrate with desired alignment using fiducials on thepackage substrate, according to an embodiment of the present invention;

FIG. 7 illustrates two fiducials placed at diagonally opposite cornersof the package substrate, according to an embodiment of the presentinvention;

FIG. 8 illustrates a flow-chart of steps during operation of the systemof 6, according to an embodiment of the present invention;

FIG. 9 illustrates a field of view of an arm camera searching toward afirst angle from a first corner of the package substrate to locate afirst fiducial, according to an embodiment of the present invention;

FIG. 10 illustrates the field of view of the arm camera searching towarda second angle from a second corner of the package substrate to locate asecond fiducial, according to an embodiment of the present invention;

FIG. 11 illustrates determining X and Y components of a distance betweena first reference point of the first fiducial and a second referencepoint of the second fiducial, according to an embodiment of the presentinvention;

FIG. 12 shows a center point of the IC die to be aligned to a centerpoint of the package substrate as determined using the first and secondreference points of the first and second fiducials, according to anembodiment of the present invention;

FIG. 13 shows a side view as the IC die is placed onto the packagesubstrate in FIG. 12, according to an embodiment of the presentinvention;

FIG. 14 illustrates alignment of the center point of the IC die to thecenter point of the package substrate for coarse alignment, according toan embodiment of the present invention;

FIG. 15 illustrates three fiducials placed at three corners of thepackage substrate, according to another embodiment of the presentinvention;

FIG. 16 illustrates the field of view of the arm camera searching towarda third angle from a third corner of the package substrate to locate athird fiducial, according to an embodiment of the present invention;

FIG. 17 illustrates a flow-chart with extended steps from the flow-chartof FIG. 8 for fine alignment during operation of the system of 6,according to a further embodiment of the present invention;

FIG. 18 illustrates a field of view of a table camera for determiningdistances of solder bumps on the IC die from edges of the IC die forfine alignment of the IC die to the package substrate, according toanother embodiment of the present invention;

FIG. 19 illustrates use of the fiducials for checking for properorientation of the IC die with respect to the package substrate,according to an embodiment of the present invention;

FIG. 20 illustrates a block diagram for attachment and reflow of the ICdie to the package substrate with visual inspection for properalignment;

FIG. 21 illustrates a block diagram for attachment and reflow of the ICdie to the package substrate with automated inspection for properalignment, according to another aspect of the present invention;

FIG. 22 illustrates a block diagram of components of the system forautomated inspection for alignment between the IC die and the packagesubstrate, according to an embodiment of the present invention;

FIG. 23 illustrates a flow-chart of steps during operation of the systemof 22, according to an embodiment of the present invention;

FIG. 24 illustrates an imaged field of view from a camera in the systemof FIG. 22 with applications for determining the level of alignmentbetween the IC die and the package substrate, according to an embodimentof the present invention; and

FIG. 25 illustrates the field of view of FIG. 24 with rotationalmisalignment between the IC die and the package substrate.

The figures referred to herein are drawn for clarity of illustration andare not necessarily drawn to scale. Elements having the same referencenumber in FIGS. 1–25 refer to elements having similar structure andfunction.

DETAILED DESCRIPTION

Referring to FIGS. 6 and 13, a block diagram of a system 200 of FIG. 6includes components for placing an IC (integrated circuit) die 202 ontoa package substrate 204 with desired alignment for manufacture of an ICpackage 205 of FIG. 13, according to an embodiment of the presentinvention. The IC die 202 has a plurality of solder bumps formed on abottom surface 203 (similar to the solder bumps 106A-1061 described inreference to the IC die 102 of FIG. 1) to be mounted to a plurality ofcircular pads exposed on a top surface 220 of the package substrate 204(similar to the circular pads 108A–108I described in reference to thepackage substrate 104 of FIG. 1).

The system 200 includes a data processor 206 and a data storage device208. The data processor 206 is coupled to the data storage device 208that stores data and instructions to be executed by the data processor206 and that may also store temporary variables during execution ofinstructions by the data processor 206. For example, the data processor206 and the data storage device 208 may be components of a computersystem that is in general individually known to one of ordinary skill inthe art. The data storage device 208 may include a static storage deviceof the computer system such as a ROM (read only memory) device, a mainmemory of the computer system such as a RAM (random access memory)device, and/or any other type of data storage device such as a floppydisc or a compact disc, as generally known to one of ordinary skill inthe art.

In addition, the system 200 includes an arm camera 210 for generating animage of a field of view of the package substrate 204. An arm cameraservo 217 is coupled between the arm camera 210 and the data processor206 for controlling movement of the arm camera 210. The data processor206, the arm camera 210, and the arm camera servo 217 comprise a firstrobotic vision tool. Similarly, the system 200 includes a table camera211 for generating an image of a field of view of solder bumps on the ICdie 202. A table camera servo 213 is coupled between the table camera211 and the data processor 206 for controlling movement of the tablecamera 211. The data processor 206, the table camera 211, and the tablecamera servo 213 comprise a second robotic vision tool.

Furthermore, the system 200 includes a robotic arm 214 for handling theIC die 202 and for carrying the arm camera 210. A robotic arm servo 216is coupled between the robotic arm 214 and the data processor 206 forcontrolling movement of the robotic arm 214. Additionally, an alarmgenerator 218 is coupled to the data processor 206. The components 210,211, 212, 213, 214, 216, 217, and 218 in the system 200 are in generalindividually known to one of ordinary skill in the art.

FIG. 7 shows a view of a top surface 220 of the package substrate 204having an area of a cage 222 with a plurality of circular pads exposedthereon (similar to the top surface 110 of the package substrate 104 inFIG. 1). However, the top surface 220 of the package substrate 204according to an embodiment of the present invention additionallyincludes a first fiducial 224 located at a first location that is towardan upper left corner 226 of the package substrate 204. Additionally, thetop surface 220 of the package substrate 204 also includes a secondfiducial 228 located at a second location that is toward a lower rightcorner 230 of the package substrate 204.

In the embodiment of FIG. 7, the first and second fiducials 224 and 228are disposed on diagonally opposite corners 226 and 230 of the packagesubstrate 204. The first fiducial 224 includes a first corner dot 232and first side dots 234 and 236. Each of the first side dots 234 and 236is displaced from the first corner dot 232 by a first distance 238. Inaddition, the first fiducial 224 is configured with the first corner dot232 being located as a corner of an “L” and with the two first side dots234 and 236 being located as end-points of the “L”. Furthermore, a lineformed from the center of the first corner dot 232 to the center of one234 of the first side dots forms a right angle (i.e., a 90° angle) withrespect to a line formed from the center of the first corner dot 232 tothe center of the other 236 of the first side dots.

Similarly, the second fiducial 228 includes a second corner dot 242 andsecond side dots 244 and 246. Each of the second side dots 244 and 246is displaced from the second corner dot 242 by a second distance 248. Inone embodiment of the present invention, the second distance 248 betweeneach of the second side dots 244 and 246 and the second corner dot 242for the second fiducial 228 is different from the first distance 238between each of the first side dots 234 and 236 and the first corner dot232 for the first fiducial 224.

Also, the second fiducial 228 is configured with the second corner dot242 being located as a corner of an “L” and with the two second sidedots 244 and 246 being located as end-points of the “L”. Furthermore, aline formed from the center of the second corner dot 242 to the centerof one 244 of the second side dots forms a right angle (i.e., a 90°angle) with respect to a line formed from the center of the secondcorner dot 242 to the center of the other 246 of the second side dots.

In an embodiment of the present invention, the circular pads within thecage 222 and the dots 232, 234, 236, 242, 244, and 246 of the first andsecond fiducials 224 and 228 each have a same diameter 250. In anexample embodiment of the present invention, each of the circular padswithin the cage 222 and each of the dots 232, 234, 236, 242, 244, and246 of the first and second fiducials 224 and 228 have a diameter 250 ofabout 100 μm (micrometers).

In that example embodiment, the first distance 238 between each of thefirst side dots 234 and 236 and the first corner dot 232 is about 0.25mm (milli-meter) for the first fiducial 224. The second distance 248between each of the second side dots 244 and 246 and the second cornerdot 242 is about 0.45 mm for the second fiducial 228. In addition, thedots 232, 234, 236, 242, 244, and 246 of the first and second fiducials224 and 228 are disposed outside the cage 222 having the circular padsof the package substrate 204 therein.

FIG. 8 shows a flow-chart of steps performed by the data processor 206of FIG. 6 from execution of instructions stored in the data storagedevice 208 for using the fiducials 224 and 228 to align the IC package202 to the package substrate 204, according to an embodiment of thepresent invention. Referring to FIGS. 6, 8, and 9, the data processor206 controls the arm camera servo 217 to move the arm camera 210 suchthat a field of view 252 of the arm camera 210 starts at the upper leftcorner 226 of the package substrate 204.

In addition, the arm camera 210 is controlled such that the field ofview 252 moves in a first direction (as illustrated by arrow 254 in FIG.9) inward toward the center of the package substrate 204 from the upperleft corner 226. The arm camera 210 captures the image within the fieldof view 252 and sends such an image to the data processor 206.

The data processor 206 analyzes the image of the field of view 252 fromthe arm camera 210 to locate the first corner dot 232 and the two firstside dots 234 and 236 of the first fiducial 224 (step 302 of FIG. 8).For example, the data processor 206 searches for the two first side dots234 and 236 each displaced from the first corner dot 232 by the firstdistance 238 within the imaged field of view 252 to determine that thefirst fiducial 224 is found. Applications such as image recognitionsoftware for analyzing images from a camera in general are individuallyknown to one of ordinary skill in the art.

If the data processor 206 cannot find the first fiducial 224 from theimaged field of view 252 in such a manner within a predetermined timeperiod (step 304 of FIG. 8), the data processor 206 generates an alarmwith the alarm generator 218 (step 306 of FIG. 8). The alarm generator218 may generate a visual alarm such as a flashing light or an errormessage on a GUI (graphical user interface) display or an audio alarmsuch as siren sounds for example.

When such an alarm is generated, an operator manually assists in themovement of the arm camera 210 until the three dots 232, 234, and 236 ofthe first fiducial 224 are within the field of view 252 of the armcamera 210. With such manual assistance, the data processor 206 locatesthe first fiducial 224 when the dots 232, 234, and 236 of the firstfiducial 224 are placed within the field of view 252 of the arm camera210 by the operator.

In any case, after the data processor 206 locates the first fiducial224, the data processor 206 sets a first reference point 262 as a centerof the first corner dot 232 of the first fiducial 224 (step 308 of FIG.8). In addition, after the data processor 206 finds the first fiducial224, the data processor 206 stores an image file in the data storagedevice 208 recording information such as the dimensions and locations ofthe dots 232, 234, and 236 comprising the first fiducial 224.

Similarly, referring to FIG. 10, the data processor 206 controls the armcamera servo 217 to move the arm camera 210 such that the field of view252 of the arm camera 210 starts at the lower right corner 230 of thepackage substrate 204. In addition, the arm camera 210 is controlledsuch that the field of view 252 moves in a second direction (asillustrated by arrow 256 in FIG. 10) inward toward the center of thepackage substrate 204 from the lower right corner 230.

The data processor 206 analyzes the image of the field of view 252 fromthe arm camera 210 to locate the second corner dot 242 and the secondside dots 244 and 246 of the second fiducial 228 (step 310 of FIG. 8).For example, the data processor 206 searches for the two second sidedots 244 and 246 each displaced from the second corner dot 242 by thesecond distance 248 within the imaged field of view 252 to determinethat the second fiducial 228 is found.

If the data processor 206 cannot find the second fiducial 228 from theimaged field of view 252 in such a manner within a predetermined timeperiod (step 312 of FIG. 8), the data processor 206 generates an alarmwith the alarm generator 218 (step 314 of FIG. 8). When such an alarm isgenerated, an operator manually assists in the movement of the armcamera 210 until the three dots 242, 244, and 246 of the second fiducial228 are within the field of view 252 of the arm camera 210. With suchmanual assistance, the data processor 206 locates the second fiducial228 when the dots 242, 244, and 246 of the second fiducial 228 areplaced within the field of view 252 of the arm camera 210 by theoperator.

In any case, after the data processor 206 locates the second fiducial228, the data processor 206 sets a second reference point 264 as acenter of the second corner dot 242 of the second fiducial 228 (step 316of FIG. 8). In addition, after the data processor 206 finds the secondfiducial 228, the data processor 206 stores an image file in the datastorage device 208 recording information such as the dimensions andlocations of the dots 242, 244, and 246 comprising the second fiducial228.

In this manner, the first robotic vision tool comprised of the dataprocessor 206, the arm camera 210, and the arm camera servo 217 locatesthe first and second fiducials 224 and 228 and determines the first andsecond reference points 262 and 264. The dots 232, 234, and 236 of thefirst fiducial 224 are distinguishable from the circular pads within thecage 222 of the package substrate 204 because of the distinct firstdistance 238 and positions of the fist side dots 234 and 236 from thefirst corner dot 232. Similarly, the dots 242, 244, and 246 of thesecond fiducial 228 are distinguishable from the circular pads withinthe cage 222 of the package substrate 204 because of the distinct seconddistance 248 and positions of the second side dots 244 and 246 from thesecond corner dot 242.

In addition, the dots 232, 234, and 236 of the first fiducial 224 aredistinguishable from the dots 242, 244, and 246 of the second fiducial228 because the first and second fiducials 224 and 228 are disposedtoward diagonally opposite corners 226 and 230 of the package substrate204. In addition, the first and second fiducials 224 and 228 aredistinguishable because the first distance 238 between each of the firstside dots 234 and 236 and the first corner dot 232 for the firstfiducial 224 is different from the second distance 248 between each ofthe second side dots 244 and 246 and the second corner dot 242 for thesecond fiducial 228.

Referring to FIGS. 8 and 11, after the data processor 206 determines thefirst and second reference points 262 and 264 for the first and secondfiducials 224 and 228, the data processor 206 determines an X-component272 and a Y-component 274 of the distance between the first and secondreference points 262 and 264 (step 318 of FIG. 8). The data processor206 then determines whether each of the X-component 272 and theY-component 274 are within a respective acceptable range (step 320 ofFIG. 8).

The respective acceptable range for each of the X-component 272 and theY-component 274 are determined from the CAD (computer assisted design)dimensions selected during design for forming the first and secondfiducials 224 and 228 on the package substrate 204. For example, therespective acceptable range for the X-component 272 may be 5.0 mm(milli-meters) ±0.2 mm, and the respective acceptable range for theY-component 274 may be 4.0 mm (milli-meters) ±0.2 mm.

If the data processor 206 determines that any of the X-component 272 andthe Y-component 274 is not within the respective acceptable range, thedata processor 206 generates an alarm with the alarm generator 218 (step322 of FIG. 8) and ends operation. Such an alarm indicates that the ICdie 202 may not be aligned to the package substrate 204 within anacceptable level.

Thus, the operator is notified of such a faulty condition such thatattachment of the IC die 202 onto the package substrate 204 with suchunacceptable misalignment is prevented. Upon generation of the alarm, anoperator may reset the system 200 such that the data processor 206 mayre-attempt to determine the first and second reference points from thefirst and second fiducials 224 and 228. Alternatively, the operator mayattempt to determine and correct for the underlying cause that led tothe unacceptable misalignment.

On the other hand, referring to FIGS. 8 and 12, if the data processor206 determines that each of the X and Y components 272 and 274 arewithin the respective acceptable range (step 320 of FIG. 8), the dataprocessor 206 determines a center point 282 of the package substrate 204as the intersection point between a first substrate line 284 runningperpendicular to the mid-point of the X-component 272 and a secondsubstrate line 286 running perpendicular to the mid-point of theY-component 274 (step 324 of FIG. 8).

Referring to FIGS. 12 and 13, for placing the IC die 202 onto thepackage substrate 204 with desired alignment, a center point 292 of atop surface 288 of the IC die 202 is determined. The top surface 288 ofthe IC die 202 is opposite to the bottom surface 203 of the IC die 202having the solder bumps formed thereon. The center point 292 of the ICdie 202 is determined as the intersection point between a first die line294 running perpendicular to the mid-point of an X-dimension 295 of thetop surface 288 of the IC die 202 and the second die line 296 runningperpendicular to the mid-point of a Y-dimension 295 of the top surface288 of the IC die 202.

Referring to FIGS. 12, 13, and 14, the data processor 206 controls therobotic arm servo 216 to move the robotic arm 214 carrying the IC die202 onto the package substrate 204. The robotic arm 214 places thebottom surface 203 of the IC die 202 having solder bumps formed thereonto face the upper surface 220 of the package substrate 204 havingcircular pads exposed thereon.

In addition, as the robotic arm 214 places the IC die 202 onto thepackage substrate 204, the center point 292 of the IC die 202 and thefirst and second die lines 294 and 296 are formed by the data processor206 onto the image of the IC die 202 within the field of view of the armcamera 210. Furthermore, the data processor 206 forms the center point282 of the package substrate 204 and the first and second substratelines 284 and 286 onto the image of the package substrate 204 within thefield of view of the arm camera 210.

For aligning the IC die 202 to the package substrate 204, the dataprocessor 206 controls the robotic arm 214 via the robotic arm servo 216to move the IC die 202 with respect to the package substrate 204 untilthe center point 292 of the IC die 202 is on top of the center point 282of the package substrate 204 as illustrated in FIG. 14 (step 326 of FIG.8). In addition, for rotational alignment, the data processor 206controls the robotic arm 214 to move the IC die 202 until the first dieline 294 is aligned to the first substrate line 284 and/or until thesecond die line 296 is aligned to the second substrate line 286 asillustrated in FIG. 14.

In this manner, the data processor 206, the robotic arm servo 216, andthe robotic arm 214 comprise a robotic placement mechanism for placingthe IC die 202 onto the package substrate 204. Furthermore, thefiducials 224 and 228 are used by the first robotic vision tool and therobotic placement mechanism to place the IC die 202 onto the packagesubstrate 204 with desired alignment. With such alignment, solder bumpsof the IC die 202 are aligned to the circular pads of the packagesubstrate 204 for minimized resistance through the couplings of thesolder bumps to the circular pads.

After the IC die 202 is placed onto the package substrate 204 with suchalignment, a die attach is used for holding the IC die 202 to thepackage substrate 204 with such alignment. Then, a reflow process isperformed to join the solder bumps of the IC die 202 to the circularpads of the package substrate 204. Such a die attach and such a reflowprocess are in general individually known to one of ordinary skill inthe art.

Verification that each of the X and Y components 272 and 274 between thereference points 262 and 264 is within the respective acceptable rangeensures that any misalignment between the IC die 202 and the packagesubstrate 204 is less than an undesirable level. In addition, thefiducials 224 and 228 are comprised of dots 232, 234, 236, 242, 244, and246 having a same size as the circular pads on the package substrate 204to provide more accurate alignment from consistency between the size ofthe reference markings (i.e. the dots of the fiducials 224 and 228) andthe objects to be aligned (i.e., the solder bumps of the IC die 202 andthe circular pads of the package substrate 204).

The foregoing is by way of example only and is not intended to belimiting. Any numbers specified herein are by way of example only. Forexample, the present invention may be practiced with any number offiducials having any number of dots with any type of references at otherlocations aside from the example of the reference points 262 and 264. Inaddition, the fiducials may be comprised of any other type of markingshaving different appearances from the three dots illustrated asembodiments of the present invention herein. Furthermore, any dimensionsspecified herein are by way of example only. Additionally, the presentinvention may also be practiced when the solder bumps on the IC die 202and the pads of the package substrate 204 have different shapes anddimensions with correspondingly different shapes and dimensions of thefiducial markings from the circular examples illustrated and describedherein.

FIG. 15 illustrates an alternative embodiment of the package substrate204 having an additional third fiducial 350 in addition to the first andsecond fiducials 224 and 228 of FIG. 7. FIG. 17 illustrates a flowchartof additional steps from the flowchart of FIG. 8 using the thirdfiducial 350 for ensuring further alignment between the IC die 202 andthe package substrate 204.

Referring to FIG. 15, the third fiducial 350 is placed at a third corner352 of the package substrate 204. The third fiducial 350 is similar tothe first fiducial 224 and is comprised of a third corner dot 354 andthird side dots 356 and 358. Similar to the dots of the first fiducial224, each of the third side dots 356 and 358 is displaced from the thirdcorner dot 354 by the first distance 238 for the third fiducial 350.

In addition, the third fiducial 350 is configured with the third cornerdot 354 being located as a corner of an “L” and with the two third sidedots 356 and 358 being located as end-points of the “L”. Furthermore, aline formed from the center of the third corner dot 354 to the center ofone 356 of the third side dots forms a right angle (i.e., a 90° angle)with respect to a line formed from the center of the third corner dot354 to the center of the other 358 of the third side dots.

Referring to FIGS. 8 and 17, the first and second reference points 262and 264 of the first and second fiducials 224 and 228, respectively, aredetermined according to the steps of the flowchart of FIG. 8 as alreadydescribed herein (step 370 of FIG. 17). In addition, referring to FIGS.6, 16, and 17, the data processor 206 controls the arm camera servo 217to move the arm camera 210 such that the field of view 252 of the armcamera 210 starts at the lower left corner 352 of the package substrate204. In addition, the arm camera 210 is controlled such that the fieldof view 252 moves in a third direction (as illustrated by arrow 360 inFIG. 16) inward toward the center of the package substrate 204 from thelower left corner 352.

The data processor 206 analyzes the imaged field of view 252 from thearm camera 210 to locate the third corner dot 354 and the third sidedots 356 and 358 of the third fiducial 350 (step 372 of FIG. 17). Forexample, the data processor 206 searches for the two third side dots 356and 358 each displaced from the third corner dot 354 by the firstdistance 238 within the imaged field of view 252 to determine that thethird fiducial 350 is found.

If the data processor 206 cannot find the third fiducial 350 from theimaged field of view 252 in such a manner within a predetermined timeperiod (step 374 of FIG. 17), the data processor 206 generates an alarmwith the alarm generator 218 (step 376 of FIG. 17). When such an alarmis generated, an operator manually assists in the movement of the armcamera 210 until the three dots 354, 356, and 358 of the third fiducial350 are within the field of view 252 of the arm camera 210. With suchmanual assistance, the data processor 206 locates the third fiducial 350when the dots 354, 356, and 358 of the third fiducial 350 are placedwithin the field of view 252 of the arm camera 210 by the operator.

In any case, after the data processor 206 locates the third fiducial350, the data processor 206 sets a third reference point 362 as a centerof the third corner dot 354 of the third fiducial 350 (step 378 of FIG.8). In addition, after the data processor 206 finds the third fiducial350, the data processor 206 stores an image file in the data storagedevice 208 recording information such as the dimensions and locations ofthe dots 354, 356, and 358 comprising the third fiducial 350.

Referring to FIGS. 16 and 17, after the data processor 206 determinesthe first, second, and third reference points 262, 264, and 362 for thefirst, second, and third fiducials 224, 228, and 350, respectively, thedata processor 206 determines the X-component 272 and the Y-component274 (step 380 of FIG. 17). In FIG. 16, the X-component 272 is determinedas the distance between the second and third reference points 264 and362, and the Y-component 274 is determined as the distance between thefirst and third reference points 262 and 362. Such X and Y components272 and 274 are more accurately determined in the embodiment of FIG. 16using the three reference points 262, 264, and 362.

The data processor 206 then determines whether each of the X-component272 and the Y-component 274 is within a respective acceptable range(step 382 of FIG. 17) similar to step 320 of FIG. 8. If the dataprocessor 206 determines that any of the X and Y components 272 and 274is not within the respective acceptable range, the data processor 206generates an alarm with the alarm generator 218 (step 384 of FIG. 17)and ends operation similar to step 322 of FIG. 8.

Referring to FIGS. 14, 16, and 17, if the data processor 206 determinesthat each of the X and Y components 272 and 274 is within the respectiveacceptable range (step 382 of FIG. 17), the data processor 206determines the center point 282 of the package substrate 204 from the Xand Y components 272 and 274 in FIG. 16 (step 386 of FIG. 17) similar tostep 324 of FIG. 8. In addition, the center point 292 and the die lines294 and 296 of the IC die 202 are aligned to the center point 282 andthe substrate lines 284 and 286 of the package substrate 204 duringplacement of the IC die 202 onto the package substrate 204 (step 388 ofFIG. 17) similar to step 326 of FIG. 8.

In a further embodiment of the present invention, alignment of thecenter point 292 and the lines 294 and 296 of the IC die 202 to thecenter point 282 and the lines 284 and 286 of the package substrate 204is considered coarse alignment. Referring to FIGS. 6, 17, and 18, forfine alignment, the table camera 211 is used to for generating a fieldof view 390 of solder bumps 106A, 106B, 106C, 106D, 106E, 106F, 106G,106H, and 106I on the bottom surface 203 of the IC die 202 (step 389 ofFIG. 17). The data processor 206 controls movement of the table camera211 via the table camera servo 213 until predetermined solder bumps 106Aand 106G near edges 392 and 394 of the IC die 202 are within the imagedfield of view 390.

The data processor 206 analyzes the imaged field of view 390 from thetable camera 211 to determine a first distance 396 between the firstedge 392 of the IC die 202 and a center of the first solder bump 106G.In addition, the data processor 206 also determines a second distance398 between the second edge 394 of the IC die 202 and a center of thesecond solder bump 106A. The data storage device 208 has stored thereindesired values for the distances 396 and 398.

The data processor 206 subtracts the desired values for the distances396 and 398 to those measured from the imaged field of view 390 todetermine distance offsets. Such distance offsets may result for examplefrom variance during formation of the solder bumps 106A-1061 on the ICdie 202. The data processor 206 uses such distance offsets to controlmovement of the robotic arm 214 carrying the IC die 202 via the roboticarm servo 216 for fine adjustment of the alignment of the IC die 202with respect to the package substrate 204 (step 389 of FIG. 17). In thismanner, the second robotic vision tool comprised of the data processor206, the table camera 211, and the table camera servo 213 is used forfine alignment of the IC die 202 with respect to the package substrate204.

In another embodiment of the present invention, referring to FIGS. 17and 19, the fiducials 224, 228, and 350 are used for checking for properorientation of the IC die 202 with respect to the die package 204.Referring to FIG. 15, the second fiducial 228 is distinguishable fromthe first and third fiducials 224 and 350 because the distance 248 ofthe side dots 244 and 246 from the corner dot 242 is greater than such adistance 238 for the first and third fiducials 224 and 350.

The IC die 202 includes an orientation marking 400 thereon that isnearest to the second fiducial 228 of the three fiducials 224, 228, and350 when the IC die 202 is placed onto the package substrate 204 withproper orientation. Because the second fiducial 228 is distinguishablefrom the first and third fiducials 224 and 350, the second fiducial 228on the package substrate 204 and the orientation marking 400 on the ICdie 202 are used to check for proper orientation of the IC die 202 withrespect to the package substrate 204 (step 402 of FIG. 17).

The arm camera 210 may be used to image a field of view near the secondfiducial 228. If the orientation marker 400 of the IC die 202 is nearthe second fiducial 228, then the IC die 202 has proper orientation withrespect to the package substrate 204. If the orientation marker 400 ofthe IC die 202 is not near the second fiducial 228, then the IC die 202is not properly orientated with respect to the package substrate 204.

If the data processor 206 determines that the IC die 202 is not properlyoriented with respect to the package substrate 204 (step 402 of FIG.17), the data processor 206 generates an alarm with the alarm generator218 and ends operation (step 404 of FIG. 17). Thus, the operator isnotified of such a faulty condition such that attachment of the IC die202 onto the package substrate 204 with such wrong orientation isprevented. On the other hand, if the data processor determines that theIC die 202 is properly oriented with respect to the package substrate204 (step 402 of FIG. 17), the operation of the system 200 of FIG. 6 foraligning the IC die 202 with respect to the package substrate 204 ends.

Referring to FIG. 20, with proper orientation and alignment ensured fromoperation of the system 200 of FIG. 6, the IC die 202 is attached to thepackage substrate 204 within a die attach system 502. The system 200 ofFIG. 6 may be part of the die attach system 502. A die attach mechanismfor attaching the IC die 202 to the package substrate 204 is in generalindividually known to one of ordinary skill in the art. For example, asticky material may be sprayed on the solder bumps of the IC die 202that are placed onto the circular pads of the package substrate 204.Alternatively, a clamping mechanism may be used to attach the IC die 202to the package substrate 204.

After such attachment of the IC die 202 to the package substrate 204,inspection is performed for ensuring proper alignment of the IC die 202with respect to the package substrate before a reflow process isperformed within a reflow furnace 504. Referring to FIGS. 13 and 20,when the IC die 202 and the package substrate 204 that are attachedtogether are placed into the reflow furnace 504, the solder bumps of theIC die 202 become molten to be electrically connected to the circularpads of the package substrate.

In FIG. 20, before such a reflow process within the reflow furnace 504,a magnifier 506 is used for visual inspection of the IC die 202 attachedon the package substrate 204. Typically, the image through the magnifier506 is magnified three times, and an operator visually inspects such amagnified image to ensure proper alignment of the IC die 202 withrespect to the package substrate 204. However, such visual inspection byan operator is prone to human error and is time consuming.

Referring to FIG. 21, in another embodiment of the present invention, anautomated die alignment inspection system 508 is used between the dieattach system 502 and the reflow furnace 504. In addition, a systemslink 510 is used for communication between the die attach system 502,the die alignment inspection system 508, and the reflow furnace 504.

FIG. 22 shows a block diagram of the die alignment inspection system 508which includes a camera 512 for generating an image of an IC package 514having the IC die 202 attached to the package substrate 204. Inaddition, the system 508 includes a data processor 516 and a datastorage device 518. The data processor 516 is coupled to the datastorage device 518 that stores data and instructions to be executed bythe data processor 516 and that may also store temporary variablesduring execution of instructions by the data processor 516.

For example, the data processor 516 and the data storage device 518 maybe components of a computer system that is in general individually knownto one of ordinary skill in the art. The data storage device 518 mayinclude a static storage device of the computer system such as a ROM(read only memory) device, a main memory of the computer system such asa RAM (random access memory) device, and/or any other type of datastorage device such as a floppy disc or a compact disc, as generallyknown to one of ordinary skill in the art.

A camera servo 520 is coupled between the camera 512 and the dataprocessor 516 for controlling movement of the camera 512. The dataprocessor 516, the camera 512, and the camera servo 520 comprise arobotic vision tool. Additionally, an alarm generator 522 is coupled tothe data processor 516. Furthermore, the data processor 516 is coupledto the systems link 510 for sending signals to the die attach system 502or the reflow furnace 504. The components 512, 516, 518, 520, and 522 inthe system 508 are in general individually known to one of ordinaryskill in the art.

FIG. 23 shows a flow-chart of steps performed by the data processor 516of FIG. 22 from execution of instructions stored in the data storagedevice 518 for automated inspection of alignment between the IC die 202and the package substrate 204, according to an embodiment of the presentinvention. Referring to FIGS. 23 and 24, the data processor 516 controlsmovement of the camera 512 via the camera servo 520 until an imagedfield of view 524 from the camera 512 includes the IC die 202 attachedto the package substrate 204.

Referring to FIGS. 14, 15, and 24, the package substrate 204 of FIG. 24is similar to FIG. 15 including the first, second, and third fiducials224, 228, and 350 disposed toward first, second, and third corners, 226,230, and 352, respectively, of the package substrate 204, as alreadydescribed herein with respect to FIG. 15. In addition, the IC die 202has been attached to the package substrate 204 similarly as illustratedin FIG. 14 within the die attach system 502, as already described hereinwith respect to FIG. 8 or 17 for the system 200 of FIG. 6.

The data processor 516 finds the first, second, and third fiducials 224,228, and 350 within the imaged field of view 524 from the camera 512(step 602 of FIG. 23). Applications such as image recognition softwarefor analyzing images from a camera by a data processor in general areindividually known to one of ordinary skill in the art. In addition, thedata processor 516 determines the first reference point 501 as thecenter point of the corner dot 232 for the first fiducial 224, thesecond reference point 503 as the center point of the corner dot 264 forthe second fiducial 228, and the third reference point 505 as the centerpoint of the corner dot 354 for the third fiducial 350 (step 604 of FIG.23).

The data processor 516 determines an X-component 507 as the distancebetween the third reference point 505 and the second reference point503, and a Y-component 509 as the distance between the third referencepoint 505 and the first reference point 501. The data processor 516 usessuch X and Y components 507 and 509 to determine the center point 511 ofthe package substrate 204 similarly as described for the center point282 in FIG. 12 (step 606 of FIG. 23).

Furthermore, the data processor 516 uses a first vertical caliper 526with an edge that is aligned to a vertical edge 528 of the IC die 202 inthe imaged field of view 524 from the camera 512. A second verticalcaliper 530 is generated in the imaged field of view 524 to be parallelwith a vertical edge 532 of the package substrate 204. Similarly, thedata processor 516 uses a first horizontal caliper 534 with an edge thatis aligned to a horizontal edge 536 of the IC die 202 in the imagedfield of view 524. A second horizontal caliper 538 is generated in theimaged field of view 524 to be parallel with a horizontal edge 540 ofthe package substrate 204. Applications such as image processingsoftware for analyzing and processing images from a camera by a dataprocessor in general are individually known to one of ordinary skill inthe art.

After the vertical edge 528 and the horizontal edge 536 of the IC die202 are found using the vertical and horizontal calipers 526 and 534,the data processor determines an X-dimension 542 and a Y-dimension 544of the IC die 202 (step 608 of FIG. 23). Furthermore, the data processor516 uses the X-dimension 542 and the Y-dimension 544 to determine acenter point 546 for the IC die 202 similarly as described for thecenter point 292 in FIG. 12 (step 608 of FIG. 23).

The data processor 516 determines whether the center point 511 of thepackage substrate 204 is aligned to the center point 546 of the IC die202 (step 610 of FIG. 23). The data processor 516 determines that thecenter point 511 of the package substrate 204 is aligned to the centerpoint 546 of the IC die 202 if the distance between the center points511 and 546 is within an acceptable range such as less than 70 μm(micro-meters) for example. The acceptable range is determined fromempirical experience of tolerance for various parameters such as dieedge variation and variation of diameters of the solder bumps on the ICdie 202 and the pads of the package substrate 204.

In another embodiment of the present invention, each of the X-componentand the Y-component for the distance between the center points 511 and546 must be within the acceptable range for the IC die 202 to be deemedacceptably aligned to the package substrate 204. Determination of the Xand Y components of a distance between two points in general isindividually known to one of ordinary skill in the art.

If the data processor 516 determines that the distance between thecenter points 511 and 546 is not within the acceptable range, the dataprocessor 516 generates an alarm with the alarm generator 522 (step 612of FIG. 23). Such an alarm indicates that the IC die 202 is notacceptably aligned to the package substrate 204. Thus, the operator isnotified of such a faulty condition such that reflow of the solder bumpson the IC die 202 onto the circular pads of the package substrate 204 isprevented.

Upon generation of the alarm, the operator removes the IC die 202 fromthe package substrate 204 and may attempt to reattach the IC die 202 tothe package substrate 204 with better alignment within the system 200 ofFIG. 6. The die attach mechanism typically allows for removal of the ICdie 202 from the package substrate 204. In contrast, reflow of thesolder bumps of the IC die 202 onto the circular pads of the packagesubstrate 204 is irreversible. Thus, inspection for proper alignment ofthe IC die 202 with respect to the package substrate 204 is performedbefore the reflow process within the reflow furnace 504.

Furthermore, the data processor 516 also communicates with the dieattach system 502 via the systems link 510 to notify the die attachsystem 502 of the unacceptable level of alignment between the IC die 202and the package substrate 204 (step 614 of FIG. 23). The die attachsystem 502 may automatically stop attaching the IC die 202 to thepackage substrate upon notification of such a faulty condition. Suchcommunication is especially advantageous when the die attach system 502and the die alignment inspection system 508 are disposed at remotelocations.

Furthermore, the data processor 516 also checks for rotational alignmentbetween the IC die 202 and the package substrate 204. FIG. 25illustrates the IC die 202 rotationally misaligned with respect to thepackage substrate in an exaggerated manner for clarity of illustration.For checking for such rotational alignment, the angles between thevertical calipers 526 and 530 and between the horizontal calipers 534and 538 are determined (step 616 of FIG. 23).

The first vertical caliper 526 is aligned along the vertical edge 528 ofthe IC die 202, and the second vertical caliper 530 is aligned to beparallel to the vertical edge 532 of the package substrate 204. The dataprocessor 516 determines a first caliper angle between the first andsecond vertical calipers 526 and 530. Similarly, the first horizontalcaliper 534 is aligned along the horizontal edge 536 of the IC die 202,and the second horizontal caliper 538 is aligned to be parallel to thehorizontal edge 540 of the package substrate 204. The data processor 516determines a second caliper angle between the first and secondhorizontal calipers 534 and 538.

The data processor 516 determines whether each of the first and secondcaliper angles is within an acceptable rotational range such as lessthan 0.5° for example (step 618 in FIG. 23). The acceptable rotationalrange is determined from empirical experience of the relationshipbetween the first and second caliper angles and acceptable alignmentbetween the solder bumps of the IC die 202 and the pads of the packagesubstrate 204.

If the data processor 516 determines that any of the first and secondcaliper angles is not within the acceptable rotational range, the dataprocessor 516 generates an alarm with the alarm generator 522 (step 620of FIG. 23). Such an alarm indicates that the IC die 202 is notrotationally aligned acceptably to the package substrate 204. Thus, theoperator is notified of such a faulty condition such that reflow of thesolder bumps of the IC die 202 onto the circular pads of the packagesubstrate 204 is prevented.

Upon generation of the alarm, the operator removes the IC die 202 fromthe package substrate 204 and may attempt to reattach the IC die 202 tothe package substrate 204 with better alignment within the system 200 ofFIG. 6. Furthermore, the data processor 516 also communicates with thedie attach system 502 via the systems link 510 to notify the die attachsystem 502 of the unacceptable level of rotational alignment between theIC die 202 and the package substrate 204 (step 622 of FIG. 23).

On the other hand, if the data processor 516 determines that the IC die202 and the package substrate 204 are acceptably aligned rotationallyand with the center points 546 and 511, the data processor 516 generatessignals for approval of the reflow process through the reflow furnace504 (step 624 of FIG. 23). Such approval from the data processor 516indicates that the IC die 202 is properly aligned with respect to thepackage substrate 204. Thus, reflow of the solder bumps of the IC die202 onto the circular pads of the package substrate 204 results in lowresistance coupling between such solder bumps and circular pads.

In this manner, the data processor 516, the camera servo 520, and thecamera 512 comprise a robotic vision tool that automatically inspectsfor alignment between the IC die 202 and the package substrate 204.Furthermore, the fiducials 224, 228, and 350 formed on the packagesubstrate are used by the robotic vision tool for such automatedinspection for alignment.

The foregoing is by way of example only and is not intended to belimiting. Any numbers specified herein are by way of example only. Forexample, the present invention may be practiced with any number offiducials having any number of dots with any type of references at otherlocations aside from the example of the reference points 501, 503, and505. In addition, the fiducials may be comprised of any other type ofmarkings having different appearances from the three dots illustrated asembodiments of the present invention herein. Furthermore, any dimensionsspecified herein are by way of example only. Additionally, the presentinvention may also be practiced with different shapes and dimensions ofthe fiducial markings from the circular examples illustrated anddescribed herein.

The present invention is limited only as defined in the following claimsand equivalents thereof.

1. A method for inspecting alignment between an IC (integrated circuit)die and a package substrate, comprising: locating a plurality offiducials on the package substrate for determining a plurality ofreferences; determining a center point of the package substrate from theplurality of references; determining whether a center point of the ICdie is aligned to the center point of the package substrate within anacceptable range; and generating an alarm for preventing reflow ofsolder bumps of the IC die onto pads of the package substrate when thecenter point of the IC die is not aligned to the center point of thepackage substrate within the acceptable range.
 2. The method of claim 1,wherein each of the fiducials is comprised of a plurality of dots. 3.The method of claim 1, wherein a first fiducial of the fiducials isdisposed toward a first corner of the package substrate, and wherein asecond fiducial of the fiducials is disposed toward a second corner ofthe package substrate.
 4. The method of claim 3, wherein the first andsecond fiducials are disposed toward diagonally opposite corners of thepackage substrate.
 5. The method of claim 4, wherein a third fiducial ofthe fiducials is disposed toward a third corner of the packagesubstrate.
 6. The method of claim 3, wherein the first fiducial iscomprised of a corner dot and two side dots, with each side dot beingdisplaced from the corner dot with a first distance.
 7. The method ofclaim 6, wherein a center of the corner dot is a first reference for thefirst fiducial.
 8. The method of claim 6, wherein the second fiducial iscomprised of a corner dot and two side dots, with each side dot beingdisplaced from the corner dot with a second distance.
 9. The method ofclaim 8, wherein a center of the corner dot for the second fiducial is asecond reference for the second fiducial.
 10. The method of claim 8,wherein the first distance of the side dots from the corner dot for thefirst fiducial is different from the second distance of the side dotsfrom the corner dot for the second fiducial.
 11. The method of claim 1,wherein the first and second fiducials are comprised of dots, each ofthe dots having a same diameter as pads of the package substrate. 12.The method of claim 1, further comprising: using edges of the IC die fordetermining the center point of the IC die.
 13. The method of claim 1,further comprising: determining whether the IC die is rotationallyaligned within an acceptable rotational range with respect to thepackage substrate.
 14. The method of claim 13, further comprising:generating an alarm for preventing reflow of solder bumps of the IC dieonto pads of the package substrate when the IC die is not rotationallyaligned within the acceptable rotational range with respect to thepackage substrate.
 15. The method of claim 13, further comprising: usingedges of the IC die for determining whether the IC die is rotationallyaligned within the acceptable rotational range with respect to thepackage substrate.
 16. A method for inspecting alignment between an IC(integrated circuit) die and a package substrate comprising: locating aplurality of fiducials on the package substrate for determining aplurality of references; determining a center point of the packagesubstrate from the plurality of references; and determining whether acenter point of the IC die is aligned to the center point of the packagesubstrate within an acceptable range; wherein each of the fiducials iscomprised of a plurality of markings with each marking having a samesize and shape as each pad on the package substrate.
 17. A system forinspecting alignment between an IC (integrated circuit) die and apackage substrate, comprising: a plurality of fiducials located on thepackage substrate for determining a plurality of references; means fordetermining a center point of the package substrate from the pluralityof references; means for determining whether a center point of the ICdie is aligned to the center point of the package substrate within anacceptable range; and means for generating an alarm when the centerpoint of the IC die is not aligned to the center point of the packagesubstrate within the acceptable range.
 18. The system of claim 17,wherein each of the fiducials is comprised of a plurality of markings.19. The system of claim 17, wherein each of the fiducials is comprisedof a plurality of dots.
 20. The system of claim 17, wherein a firstfiducial of the fiducials is disposed toward a first corner of thepackage substrate, and wherein a second fiducial of the fiducials isdisposed toward a second corner of the package substrate.
 21. The systemof claim 20, wherein the first and second fiducials are disposed towarddiagonally opposite corners of the package substrate.
 22. The system ofclaim 21, wherein a third fiducial of the fiducials is disposed toward athird corner of the package substrate.
 23. The system of claim 20,wherein the first fiducial is comprised of a corner dot and two sidedots, with each side dot being displaced from the corner dot with afirst distance.
 24. The system of claim 23, wherein a center of thecorner dot is the first reference for the first fiducial.
 25. The systemof claim 23, wherein the second fiducial is comprised of a corner dotand two side dots, with each side dot being displaced from the cornerdot with a second distance.
 26. The system of claim 25, wherein a centerof the corner dot for the second fiducial is a second reference for thesecond fiducial.
 27. The system of claim 25, wherein the first distanceof the side dots from the corner dot for the first fiducial is differentfrom the second distance of the side dots from the corner dot for thesecond fiducial.
 28. The system of claim 17, wherein the first andsecond fiducials are comprised of dots, each of the dots having a samediameter as pads of the package substrate.
 29. The system of claim 17,further comprising: means for using edges of the IC die for determiningthe center point of the IC die.
 30. The system of claim 17, furthercomprising: means for determining whether the IC die is rotationallyaligned within an acceptable rotational range with respect to thepackage substrate.
 31. The system of claim 30, further comprising: meansfor generating an alarm when the IC die is not rotationally alignedwithin the acceptable rotational range with respect to the packagesubstrate.
 32. The system of claim 30, further comprising: means forusing edges of the IC die for determining whether the IC die isrotationally aligned within the acceptable rotational range with respectto the package substrate.